1. Field of the Invention
The present invention relates to a power splitter and a power combiner mainly used for a microwave circuit.
2. Description of the Related Art
For the circuit configuration of a conventional power splitter, there is a method of combining the 3-dB directional couplers shown in FIG. 5. FIG. 5 is a four-way power splitter , in which symbol 31 denotes an input terminal, 32a to 32d denote output terminals, and 33a to 33c denote 3-dB directional couplers. Though circuit design is easy for the circuit configuration in FIG. 5, there are disadvantages that the circuit scale increases when the number of split s increases, the insertion loss increases, and only a 2.sup.n -way power splitter can be constituted.
Therefore, for the circuit configuration of a compact and small-loss four-way power splitter , there is a method of cascading the directional couplers having coupling degrees 6, 4.7, and 3 dB shown in FIG. 6. In FIG. 6, symbol 41 denotes an input terminal, 42a to 42d denote output terminals, 43 denotes a 6-dB directional coupler, 44 denotes a 4.7-dB directional coupler, and 45 denotes a 3-dB directional coupler. Operations of the four-way power splitter constituted as shown in FIG. 6 are described below.
An input signal (P) input through the input terminal 41 is first input to the 6-dB directional coupler 43, 1+L /4 the input signal (P), that is, a (P/4) signal is output to the output terminal 42a, and the remaining (3P/4) signal is input to the 4.7-dB directional coupler 44. Next, the 4.7-dB directional coupler 44 outputs 1/3 the input signal (3P/4), that is, a (P/4) signal to the output terminal 42b and inputs the remaining (P/2) signal to the 3-dB directional coupler 45. Then, the 3-dB directional coupler 45 divides the input signal (P/2) into two equal signals, outputs a (P/4) signal to output terminals 42c and 42d respectively, and operates as a four-way power splitter.
FIG. 7 shows a case in which the configuration in FIG. 6 is constituted of a conventional branch-line-shaped directional coupler. In FIG. 7, symbols 51 and 52 denote transmission lines, 53, 54, and 55 denote terminating resistors, 43a denotes an input port, 43b denotes an isolation port, 43c denotes a first output port, and 43d denotes a second output port, and a component same as that in FIG. 6 is provided with the same symbol.
In the case of the configuration in FIG. 7, however, a branch-line-shaped directional coupler having a large coupling degree is necessary when the number of split s increases. To constitute the above directional coupler, a transmission line having a high characteristic impedance or generally, a microstrip line is necessary. Thus, the configuration as problems that loss increases because the strip line width decreases and the machining accuracy is limited.